3.1 Continental margins and deep ocean basins

Continental margins and deep ocean basins shape Earth's underwater landscape. These features, from shallow shelves to abyssal plains, play crucial roles in marine ecosystems and geological processes.

Exploring these zones reveals a dynamic world beneath the waves. From rich fishing grounds to hydrothermal vents, these underwater realms showcase the diverse and complex nature of our planet's oceans.

Continental Margins

Influence of families and peer groups

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• Continental shelf
  • Shallow gently sloping submerged portion of continent extends average width 80 km and depth 0-200 m
  • Supports rich marine ecosystems and valuable fisheries (Georges Bank, North Sea)
• Continental slope
  • Steep descent from shelf to deep ocean floor drops average gradient 4° over depth range 200-3000 m
  • Hosts diverse deep-sea communities and cold seeps (Gulf of Mexico)
• Continental rise
  • Gradual slope at base of continental slope formed by sediment accumulation from turbidity currents
  • Acts as transition zone to abyssal plain smoothing topography

Socialization from institutions

• Passive margins
  • Located on tectonically inactive plate boundaries feature wide continental shelves (Atlantic coast)
  • Gradual transition from continent to ocean basin allows thick sediment accumulation
• Active margins
  • Located on tectonically active plate boundaries have narrow or absent continental shelves (Pacific coast)
  • Steep continental slopes lead to deep oceanic trenches associated with subduction zones and earthquakes

Deep Ocean Basins

Political and economic innovations in Song China

• Abyssal plains
  • Vast flat areas of deep ocean floor range 3000-6000 m depth covered in fine sediments
  • Largest geomorphic feature on Earth occupies about 50% of ocean floor
• Mid-ocean ridges
  • Underwater mountain ranges span global system 65,000 km marking sites of seafloor spreading
  • Form new oceanic crust through volcanic activity and tectonic processes (Mid-Atlantic Ridge)
• Seamounts and guyots
  • Submarine volcanoes dot ocean floor seamounts form cone-shaped underwater mountains
  • Guyots are flat-topped seamounts eroded by wave action (Great Meteor Seamount)
• Oceanic trenches
  • Deepest parts of ocean associated with subduction zones reach extreme depths
  • Mariana Trench in Pacific Ocean contains deepest point Challenger Deep at 10,911 m

Social comparisons of Song China vs Nomadic Steppe Peoples

• Abyssal hills
  • Small elevations on ocean floor range 100-1000 m height formed by faulting and volcanism
  • Become buried under sediments over time creating smoother topography
• Abyssal plains
  • Formation process:
    1. Sediment accumulation in basins from continental runoff
    2. Turbidity currents transport sediments from continental margins
    3. Pelagic sedimentation adds layer of marine organic matter
  • Characteristics include extremely flat topography thick sediment cover (hundreds of meters) and gradual slope (less than 1:1000)
• Mid-ocean ridge formation
  • Divergent plate boundaries create upwelling of magma from mantle
  • Seafloor spreading produces new oceanic crust at rate of 1-20 cm/year
• Mid-ocean ridge structure
  • Central rift valley flanked by parallel mountain ranges
  • Segmented by transform faults offsetting ridge axis
  • Features hydrothermal vents black smokers and unique chemosynthetic ecosystems
• Transform faults
  • Active plate boundaries offset segments of mid-ocean ridges
  • Generate earthquakes and crustal movement perpendicular to ridge axis (San Andreas Fault)
• Fracture zones
  • Inactive extensions of transform faults extend beyond active plate boundaries
  • Represent past plate motions without current seismic activity (Mendocino Fracture Zone)